Good topic ; with good compression you still have a good engine !
Keep it simple ! We thought it was the carbs [ similar problem on a 70 hp OMC { outboardmarine CRAP } ] ; took all afternoon to do carbs , got late dark , started the engine same problem . THERE IT WAS ! SPARKS ! The ground wire nut behind the powerpack had backed of enough for intermittent contact ! Before you give up clean all contacts then apply dielectric grease . I also ran a separate ground wire [ like on my 77 Vette ] .
If that works my birthday is March 03 LOL !